Iron oxide pigment and process of producing the same as by-products of the reductionof aromatic nitro compounds



Patented Apr. 23, 1935 IRON OXIDE PIGMENT AND PROCESS OF rnonocmo'rnnSAME AS BY-PRODUCTS OF THE REDUCTION or AROMATIC NITRO COMPOUNDS UlrichHaberland, Uerdingen, Germany, ass'ignor to I. G. FarbenindustrieAktiengesellschait,

- Frankfortmnt he-Main, Germany No Application December 19, 1931, SerialNo. 582,171. In Germany December 24,

The present invention relatesto-a process of producing iron oxidepigments-y more specifically it relates to a process in which a finelydivided ironioxide sludge suitable as a color pigment after drying orcalcining is. obtained as a by product from the reduction of aromaticnitro compounds to the: corresponding amines by means of iron and'acidoran acid reacting salt.

in the methods of producing aromatic amines from. aromatic nitro'compounds heretofore known and used from. a long time involving the useof iron and an amount of. acid insufficient to dissolve the. same or asalt exerting. an acid re-' action'due to hydrolysis, theiron serving asthe 1 reducing agent generally changes into a brownish. .black oxidewhose composition corresponds to aformula lying'between F6304 and F6203.This oxide is notuseful as acolor pigment and is of very inferiorquality on account of its slight coloring. and covering power. V Toillustrate the old process it maybe stated that in the manufacture ofaniline with every 100 parts of nitrobenzene about 100- par-ts of ir'on,8 to 10 parts of concentrated hydrochloric acid (specific gravityv1.16'). and about 100 parts of water, are employed. The reductioniscarried out byadding thefnitrobenz ene and iron to the hydrochloricacid and Water heated to about 100 at such a ratethat the temperature ofabout 100 C. ;is maintained lay-the heat of ;reaction.

When reduction is finished-,. the oily layer of ani- 1 further known,the hydrochloric acid employed inthe reduction may be substituted by amore or lessequivalent quantity of sulfuric acid, acetic acid,sulfurousacid or the likeor by a dilute sol-u-i tion i. e. an aqueoussolution containing less than 5 percent ,of a salt exerting an acidreaction due to hydrolysis such as ferrous chloride Without changing theproperties of the resulting iron oxide sludge. a

In accordance with the processes described U. S. application Serial No.385,457, filed August 12, 1929, now Patent No- 1,849, l28, and U. S.Patents 1,793,941 and 1,793,942 the reduction is carried out under suchconditions that the aque- 3. one phase of the reaction mixtur'e'is anacidas the saturatingconcentration of the respective 11 CIaims.(01134-59) salt and does not fall below the limit of .12 ercent duringthe reduction process. Undertlie conditions specified in the aforesaidpatents there remains after separating the aromatic amine obtained bythe reduction process an -iron oxide sludge which is substantially freefrom acidic residues andds adapted to form commercial iron oxidepigments, either directly or after calcination.

The present inventionis an improvement of the processes claimed in U. S.application SerialNo; 385,457, filed Au'gust'12f1929; now Patent No.11,849,428, and U.v S Patents 1,793,911 and 1,793,942. I have found thatanadditiori of: lead compounds such aslead oxide or lead salts-to thereduction'agents of the aforesaid specificstions will considerablyimprove the commercial grade of the iron oxide pigments obtainableaslay-products oi the reduction process. Ino'th'er words, my processcomprises as the principal i feature reducing an aromatic nitro compoundwith metallic iron, lead compounds arid an acid reacting concentratedaqueous solution of asal t, it being understood that the acidity of themixture should not suffice to dissolve the ironand the amount andconcentration of the salt present should be suflicient to form an ironoxide sludge adapted to form a commercial iro-r'i oxidcpig ment. Whencarrying out the reduction mine presence of lead compounds,a slurry isobtained from which after levigation, washing and drying atterziperatures'from about 100 C.v to about 200* C ferrous ferric oxidesresult having a deep and: bluish black or brownish shade which'may beconverted to bluish red or bright red iron oxidepigments by calciningthem at a temperature range from about 650 to about 800 C. and pref--erab ly at a temp'eratuieddf about Z00" C; .Ihe lead compounds may beadded in: the form: or oxides or saltsz I V. I o

The amount of lead oxide or lead salts such as plumbous oxide,plumbo-plumbic oxide, l-ead chloride, leadnitrate'. lead carbonate; leadacetate,

lead propionate, lead benzoate etc. used in there duction may varywithin wide ranges. Calculated on the quantity of metallic iron used itmay vary from about '2 percent to about'15 percent. Before calcining,the pigments obtained accord i-ng to this invention comprisesubstantiallyferric' oxidewith a small amount of ferrous oxide. Furthermore these pigments contain a lead oxide in an amount depending onthe amounts of-lead compounds employed in the reduction process.

My new brown iron oxide pigments-arehomoge neousand may: thus bedistinguished-from the:

' der.

previously known brown iron oxide pigments. A microscopic examination ofmy new pigments will show that each of their constituent particles is ofa uniform brown shade, whereas it can be readily ascertained under amicroscope that the previously known brown iron oxide pigments consistof a mixture of red, black and, in some cases, also yellow particles. Itis possible to isolate these differently colored constituents of theknownproducts by purely physical means, such, as, for ex-,

ample, levigation. In view of the homogeneous character of my newpigments, such an isolation of vari-colored constituents is not possiblein their case.

My invention is illustrated by the follow- Example- 1 I 127 parts of aferrous chloride solution of specific gravity 1.27 are heated to boilingwith 2.5 parts of lead carbonate, 150 parts of waterand 200 parts ofground iron powder are added and 200 parts of nitrobenzene are run in atthe boiling temperature. When the reduction is complete and the anilineproduced has been separated there are obtained by washing anddryingtheferrous-ferric oxide sludge formed, 240 parts of a mineral pigment ofbeautiful bluish black shade and satisfactory covering power. I

This pigment comprises 87.3 percent of ferric oxide, 3.1 percent offerrous oxide and 1.9 percent of lead calculated as plumbousoxide.

When instead of the above specified quantity of 2.5 parts of leadcarbonate 5 parts are used avaluable brown iron oxide pigment isproduced.

Calcination yields from the black product a beautiful bluish red andfrom the brown product a light, bright red pigment.

Example 2 To a mixture of 127 parts of a ferrous chloride solution ofspecific gravity 1.27 and 6 parts of lead chloride are added 200 partsof ground iron pow- Then 200 parts of nitro benzene are run in atboiling temperature. After completion of the reduction the anilineproduced is separated. The sludge obtained is levigated, washed anddried. There result 242 parts of a mineral pigment of a fine brown shadewhich possesses an excellent covering power. I

By calcining this pigmentat a temperature of 700 C. abright red ironoxide pigment is obtained.

Example 3 127 parts of a ferrous chloride solution of specific gravity1.27 are heated to boiling with 7 parts of lead acetate, 150 parts ofwater and 200 parts of ground iron powder are added and 200 parts ofnitro benzene are run in at the boiling temperature. When the reductionis complete and the aniline produced has been separated there areobtained by washing and drying the ferrous ferric oxide sludge formed241parts of a mineral pigment of beautiful brown shade and satisfactorycovering power.

Calcination yields from the brown product a beautiful bright redpigment.

Iclaim: I

1. The process which comprises reducing an aromatic nitro compound inthe presence of a lead compound with metallic iron and an acidreactingconcentrated'aqueous solution of a salt insufficient in amount todissolve the iron, separating the resulting iron oxide sludge from theresulting aromatic amino compound and purifying the iron oxide sludge bylevigation and washing.

2 The'process which comprises reducing an aromatic nitro compound in thepresence of a lead compound with metallic iron and an acidreactingconcentrated aqueous solution of a salt insufficient in amount todissolve the iron, separating the resulting iron oxide sludge from theresulting amino compoundand purifying'the iron oxidesludge bylevigation, washing out, drying and calcining.

*3. The process whichcomprises reducing an aromatic nitro, compound inthe, presence of a lead salt with metallic iron and an acid-reactingconcentrated aqueous solution of a salt insufficient in amount todissolve the iron, separating the resulting iron oxide sludge from theresulting amino compound and purifying the iron oxide sludgebylevigation and washing out.

4. The process which comprises reducing an aromatic nitrocompound in thepresence of lead carbonate with metallic iron and an acid-reactingconcentrated aqueous solution of a salt insufficient in amount todissolve the iron, separating the resulting ironoxide sludge from theresulting amino compound and purifying the iron oxide sludge bylevigation and washing out.

5. The process which comprises reducing an aromatic nitro compound inthe presence of a lead oxide with metallic iron and an acid-reactingconcentrated aqueous solution of a salt insufficient in amount todissolve the iron, separating the 'resultingiron oxide sludge from theresulting amino compound and purifying the iron oxide sludgeby'levigation and washing out.

6. The process which comprises reducing an aromatic nitro compound inthe pers'ence of a lead compound with metallic iron, an acid-reactingconcentrated aqueous solution containing at least 12 per cent of adissolved salt in an amount insufilcient to dissolve the iron,separating the resulting iron' oxide sludge from the resulting aminocompound and purifying the iron oxide sludge by levigation and washingout.

7. The process which comprises reducing an aromatic nitro compound inthe presence of a lead salt with metallic iron, an acid-reactingconcentrated aqueous solution containing at least 12 percent of adissolved salt'in an amount insufiicient to dissolve the iron,separating the resulting iron oxide sludge from the resulting aminocompound and purifying the iron oxide sludge by levigation and washingout.

8. The process which comprises reducing an aromatic nitro compound inthe presence of a lead-oxide with metallic iron, an acid-reactingconcentrated aqueous solution containing at least 12 per cent of adissolved salt in an amount insufficient to dissolve the iron,separating the resulting iron oxide sludge from the resulting aminocompound and purifying the iron oxide sludge by levigation and washingout.

9. The process which comprises reducing nitro,

benzene in the presence of lead carbonate with metallic iron, anacid-reacting concentrated aqueous solution containing at least 12percent of ferrous chloride in an amount insuflicient to dissolve theiron, separating the resulting iron oxide sludge from the resultingamino compound and purifying the iron oxide sludge by levigation andwashing out. a

10. The process which comprises reducing nitro benzene in the presenceof lead chloride with metallic iron, an acid-reacting concentratedaqueous solution containing at least 12 percent of ferrous chloride inan amount insuificient to dissolve the iron, separating the resultingiron oxide sludge from the resulting amino compound. and purifying theiron oxide sludge by levigation and washing out.

11. Metallic oxide pigments comprising a major proportion of ferricoxide and a minor proportion of ferrous oxide and an oxygen'com pound oflead, said pigments being homogeneous and having brown shades which maybe con- 10 verted by calcination into bright red shades. ULRICHHABERLAND.

